Polyester plasticizers are generally categorized as specialty-type plasticizers and comprise a wide variety of chemistries. Polymeric polyester plasticizers are produced from polyhydric alcohols (diols) esterified with dibasic acids, commonly adipic acid, in the presence of monobasic acids or alcohols. These polymeric polyesters comprise regularly alternating (repeating) units of dibasic acids and glycols (or diols), as compared to monomeric plasticizers that do not contain repeating units.
Polyester plasticizers are known in the art for use in a number of applications, such as adhesives, caulks, sealants, and polyvinyl chloride (PVC) plastisols. As do other plasticizers, polyester plasticizers provide compounded polymeric compositions with improved properties, such as low volatility, resistance to extraction, excellent flexibility, durability, and UV and heat resistance properties, among others, depending on the structure and molecular weight of the particular polyester utilized. Polymeric polyester plasticizers, in particular, offer low volatility, resistance to extraction by hydrocarbon fluids, and depending on the particular plasticizer—resistance to surface marring. As one example, polyester plasticizers used in polyvinyl chloride (PVC) have better extraction resistance properties than that achieved with most monomeric plasticizers, and they also demonstrate excellent non-migration properties in vinyl plastics.
Polyester plasticizers can be used in blends to improve the performance of standard monomeric plasticizers or as a substitute for them. They also may but are not required to be blended with various other conventional plasticizers to enhance or augment properties of polymeric compositions, including but not limited to improving solvating characteristics and compatibility and processability in plastisol applications. Suitable conventional plasticizers for use with polyester plasticizers include general purpose, specialty and/or secondary plasticizers, examples of which include without limitation phthalate esters, dibenzoate esters, phosphate esters, various adipate, azelate, oleate, succinate and sebacate compounds, terephthalate esters such as dioctyl terephthalate (DOTP), 1,2-cyclohexane dicarboxylate esters (such as Hexamoll® DINCH®), epoxy plasticizers, fatty acid esters, glycol derivatives, sulfonamides, and hydrocarbons and hydrocarbon derivatives that are often utilized as secondary plasticizers. Monobenzoates, such as isononyl benzoate, isodecyl benzoate, and 2-ethylhexyl benzoate, and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, among other plasticizers, can also be blended with polyester plasticizers.
It has been discovered that certain polyester plasticizers, in particular lower molecular weight oligomeric dibenzoates, are viable alternatives for traditional phthalate plasticizers used in adhesives, caulks, and sealants. They are also useful substitutes alone or in combination with other plasticizers in plastisol applications, including without limitation in PVC. These oligomeric dibenzoates comprise certain polyester plasticizers that are end-capped with benzoic acid esters.
In preparation, the oligomeric dibenzoates of the invention may have a portion of molecules which are not fully reacted, i.e., do not convert to dual benzoic acid end caps. As a result, shorter chain, hydroxyl (—OH) terminated molecules are formed, which are more water soluble than molecules having dual benzoic acid ester end-caps. These hydroxyl terminated compositions can, in some circumstances, be reactive. Depending on application, their use may be limited due to incompatibility with a polymer. Decreasing the concentration of residual hydroxyl-terminated molecules will improve compatibility by decreasing the percentage of molecules that are extractable by water.
By adding acetic anhydride during the preparation process of the oligomeric dibenzoates of the invention, unreacted hydroxyl groups may be eliminated or significantly reduced. Any excess acetic anhydride is removed at the end of the process. Use of acetic anhydride may also result in the formation of a polyester having hybrid benzoate/acetate ester end-caps. It has been discovered that this hybrid benzoate/acetate end-capped polyester is also a viable alternative for more traditional plasticizers in certain applications, often with improved results, even over the non-acetic anhydride-modified oligomeric polyester plasticizers of the invention.
The oligomeric polyester plasticizers of the invention are preferably based upon propylene glycol adipate and propylene glycol succinate polyesters that are dual end-capped (terminated on both ends) with esters of benzoic acid, i.e., propylene glycol/adipate/benzoate and propylene glycol/succinate/benzoate. The benzoate end-caps change the polarity of the polyesters making them very versatile plasticizers for use with a large number of polymers. Alternatively, the oligomeric polyester plasticizers of the invention preferably include those having hybrid benzoate/acetate end-caps.
The polyester plasticizers of the invention may also comprise other glycols (diols) and dibasic acids. Diol glycols useful in the inventive compositions, including without limitation 1,3-butane diol, 1,4-butane diol, 1,3-propane diol, and mixtures thereof. Useful dibasic acids include without limitation azelaic, glutaric, sebacic, phthalic and terephthalic acid. Polyesters prepared from these other diols and dibasic acids are also within the contemplation of the invention.
Applications for use of the inventive polyester plasticizers may depend on molecular weight. For example, the higher molecular weight propylene glycol adipate end-capped with benzoic acid esters functions well as a substitute for industry standard phthalates in polysulfide or other sealant and caulk applications, as well as in vinyl applications. The lower molecular weight propylene glycol succinate end-capped with benzoic acid esters also performs well in vinyl applications. None of these oligomeric dibenzoates are known to have been used in these applications heretofore. Surprisingly, these oligomeric dibenzoates function as well or better than traditional higher molecular weight phthalate plasticizers.
It has also been found that the inventive polyesters having hybrid benzoate and acetate ester end caps are less prone to water extraction and reactivity in certain use applications. This will result in better and longer term performance in PVC applications where exposure to weathering is expected. Since it does not extract easily, it will perform better as a plasticizer as it will continue to soften the polymer.
The inventive polyester plasticizers may be derived from natural sources, making them highly desirable from an environmental perspective.
It is an object of the invention to provide novel plasticizers comprising polyesters end-capped with dual benzoate esters or hybrid benzoate/acetate esters, which are useful in a wide variety of applications where plasticizers are traditionally used.
It is a further object of the invention to provide novel polyester plasticizers that may be used as alternatives to traditional phthalate or other traditional plasticizers in adhesives, caulks, sealants, plastisols, vinyl compositions, and other polymeric dispersions.
Yet another object of the invention is to provide adhesive, caulk, sealant, vinyl and other polymeric compositions utilizing the novel polyester plasticizers of the invention.
Still another object of the invention is to provide novel polyester plasticizers that may be blended with traditional plasticizers to improve properties of both the plasticizer and the polymeric compositions in which the blends are used.
Still a further object of the invention is to provide novel polyester plasticizers that achieve comparable or improved compatibility, processability, extraction resistance, hardness, strength, surface energy retention, volatility, and migration characteristics over traditional plasticizers used in polymeric compositions.
Other objects of the invention will be evident to one skilled in the art.